As I said earlier, it's not about "getting to the fun" faster than someone else
. It's about getting to the fun faster than you
would if you didn't pay.
Let's not trick ourselves: PvE is about achieving goals (both the process and the end). When you are going into a dragon's den to kill it, it's about the end fight because that's your entire reason for going in there, but it's also about the path getting there.
However, for some goals the process kind of isn't important. Leveling is such a goal: you don't care about going from 328768 xp to 328769 xp. You care about the one xp point that will get you to the next level, or to the max level.
It's not about how much
boost these items give. It's about that they give